Underwater Acoustic Trigger / On-Off Switch

[coldwaterak]

To keep things simple to start with I was hoping for some ideas to simply activate a switch remotely underwater.  Avoiding density, transmission distance, etc...   what are some options (reasonably cheap) to achieve turning on a light for instance in the other end of a swimming pool?

[cyberfish]

Regular RF chips?

[SmAsH]

Regular RF chips?

RF doesn't work too well through water.

@ts, Have you considered having the receiver out of the water and a wire to the device, or even just the antenna out of the water?

[cyberfish]

Ah, I didn't know that. Thanks.

[coldwaterak]

Sorry to mention...   both transmitter and receiver are under water.   

Example: blinking light for signal, photoelectric sensors to trigger switch.

This example would work great, but again it needs to be acoustic.

[Soeren]

Hi,

To keep things simple to start with I was hoping for some ideas to simply activate a switch remotely underwater.  Avoiding density, transmission distance, etc...   what are some options (reasonably cheap) to achieve turning on a light for instance in the other end of a swimming pool?

Cheap, acoustic and in-water (under water is hard to do ) put together are some tough requirements.
If you by acoustic mean human audible, I'd say your chances are next to none, but if you up the frequency to US and find some waterproof transducers, it should be possible. Submarine sonars do work after all.

Why does it need to be acoustic?

[madsci1016]

This is a tough one.

It seems easy, you are not sending data or anything. The problem arises when you have to design a system that will only respond when it's suppose too.

I'll give you an example.

I work with underwater robotics, and I work with underwater acoustics. One of the underwater navigation systems works by single pings from acoustic transponder in known locations. Measure time of flight, triangulate, and you have your position. And these work at human audible frequency, and have ranges of kilometers.

One issues the system ran into early on was interference from snapping shrimp. The receiver could not make out if it was a ping from a transponder over the noise of snapping shrimp. The fix was to encode the pulse, so it stood out as a verifiable pattern over the noise.

So if you make a system for your pool, you will have to design it such that there is some method of verifying the source of the acoustic energy, so your 'light' doesn't come on when someone jumps in the pool.

[coldwaterak]

Thanks for the posts...   Funny enough I work with underwater robotics as well Madsci, so we should be on the same page with what I'm trying to achieve.  Stepping out of the pool lets consider that this idea is going to have applications in the open ocean.  Apply voltage to a circuit, transmit, receive, activate switch.

You're dead on with the simplicity of it, no data, just a simple trigger.  Much like how you all ping your responders or an acoustic release.  But back to cost...  taking apart a $15k beacon to get the parts out of it just isn't practical.

It seems to me that with a set signal frequency and duration you could really narrow down the interference.

Anyone ever seen any acoustic transmitters/receivers from a component vendor?

[coldwaterak]

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